This paper illustrates the role of professional learning in building teacher confidence, and explicates how confidence relates to professional capital. It reports on data from the Victorian State-wide Professional Mentoring Program for Early Childhood Teachers (2011–2014), and focuses on the experiences of both new to the profession and professionally isolated early childhood teachers and their more experienced early childhood teacher mentors who participated in this purposely designed program. The findings show that participants' gains in confidence are aligned with expansions in professional capital encompassing the acquisition of knowledge and skills (human capital), participation in networks of collaborative learning communities (social capital), and the ability to exercise professional agency (decisional capital). We conclude that teacher confidence is a function – and a constitutive feature – of teacher professional capital, and that professional learning through mentoring is one way of building this vital professional attribute. Theoretical insights and empirical evidence on this intricate interconnection have strong implications for policy and practice.